This invention relates to torque limiting devices and more specifically a gear having a torque limiting clutch used in a power transmission gear train.
Household appliances use subfractional horsepower electric motors to operate mechanisms for performing a variety of appliance functions. For example a refrigerator freezer icemaker uses a subfractional horsepower motor to operate a harvest rake for ejecting ice cubes, and a cam-operated timer control uses a subfractional horsepower motor to rotate a camstack for switching appliance functions. Subfractional horsepower motors used in appliances typically use a gear train to slow rotational speed and multiply torque to operate appliance mechanisms. Appliance devices driven by subfractional horsepower motors can encounter restrictions such as when an icemaker harvest rake encounters ice cubes that do not immediately eject, or an appliance operator manually operates an icemaker harvest rake, or when an appliance operator rotates a control knob to set a cam-operated timing mechanism. If an appliance device driven by a motor becomes obstructed in some manner, the torque delivered through the gear train can become great enough to strip gear teeth causing damage to the appliance, gear train, or motor.
Torque limiting clutches have been used for many years in household appliances such as in a refrigerator freezer icemakers and cam-operated timers for such appliances as clothes dryers, clothes washing machines, and dishwashers to prevent a temporary obstruction from damaging the appliance, gear train, or motor.
Some previous appliance clutches have used flexible fingers on an annular member to engage lugs on another annular member. Such a design typically provides a uni-directional clutch. When the torque applied exceeds a predetermined value the flexible fingers flex to store energy and then release from the lugs nearly instantaneous to permit slippage. Both the flexible fingers and lugs are often shaped with thin or sharp edges that have a propensity to vibrate particularly when the flexible finger disengages from a lug and quickly release energy. The energy released includes components that vibrate at audio frequencies that can be heard near the appliance, typically in a home. Additionally fine structure such as flexible fingers can increase production cost. An appliance clutch employing a flexible finger design is disclosed in U.S. Pat. No. 5,088,581 issued to Duve.
Some previous appliance clutches have used spring biased lobes on an annular member to engage sharp teeth on another annular member. Such a design provides a bi-directional clutch. When the torque applied to one of the annular members exceeds a predetermined valve, the spring biased lobes flex to disengage from the sharp teeth to permit slippage. Disengagement and reengagement of the lobes from the sharp teeth can cause vibration at audio frequencies that can be heard near the appliance. An appliance clutch employing spring biased lobes and sharp teeth is disclosed in U.S. Pat. No. 4,702,122 issued to Richard.
Some previous appliance clutches have employed metal spring discs with protuberances that engage slots formed in a wheel well. Both the protuberances and the slots are shallow, so there is limited spring flexing space for the metal spring discs to store energy. The metal spring discs are constructed from thin sheet metal. The protuberances engaging and disengaging from slots can cause the metal to vibrate at an audio frequency. An appliance clutch employing spring discs with protuberances that engage slots formed in a wheel well is disclosed in U.S. Pat. No. 3,797,621 issued to James.
Some previous ice maker have used a one-way clutch in a drive train between a motor and harvest rake mechanism. Although a one-way clutch will permit slippage if the harvest rake encounters an obstruction, if a person manually operates the harvest rake in an attempt for instance to dislodge it from an obstruction the person may move the harvest rake in a direction opposite normal operation possibly causing damage to the harvest rake motor or drive train. An ice maker that uses a one-way clutch is disclosed in U.S. Pat. No. 4,835,978 issued to Cole.
Previous appliance clutches such as those used in appliances such as icemakers and in cam-operated timers perform a torque limiting function but can be noisy when slipping. Additionally some previous clutches used in appliances such as an ice maker are only operational in one direction. What is needed is an appliance clutch that is quieter when slipping, bi-directional, easy to manufacture, and easy to change the predetermined torque limit by varying component design.